It was supposed to be the stay-at-home year, when millions of Britons chose not to fly abroad but to bask in the British sunshine – but of course it didn’t turn out like that.

For those left in any doubt about this summer’s weather, the release of official figures yesterday proved that it has been one of the wettest and dullest on record. And it is about to get worse. Some of the most dramatic thunder and lightning storms of the year are expected tomorrow, bringing the risk of flooding, large hailstones and even tornados.

Met Office statistics show rainfall this summer is already up to 50 per cent higher than normal and August is on course to have the fewest hours of sunshine since records began.

The average rainfall across the UK from June 1 to August 26 is 317.7mm, 40 per cent more than normal, with five days of readings still to be considered. The wettest summer since records began in 1914 was in 1956 when 358.4mm fell, while last year 357.1mm was recorded.

This month is also expected to be one of the dullest since sunshine records began in 1929. The national average of 96.3 sunshine hours up to August 26 is already 40 per cent below the month’s average. The previous dullest August was in 1942, with 111.4 hours.

Hot days were also scarce, with the mercury climbing over 30C (86F) only twice. In contrast, 2006 was a scorcher, with 20 days over 30C and a top temperature of 36.5C (98F). However, the national summer temperatures this year were higher than average, 14.3C, up 0.2C on the usual 14.1C.

The awful summer has been blamed on jet stream winds delivering weather more usually seen in Iceland.

Helen Chivers, a Met Office forecaster, said: “It drives weather systems in the northern hemisphere and is normally located between Iceland and northern Scotland – but this summer, it’s been over England, Wales and France.”

Today is expected to be very warm with temperatures peaking at 27C but the meteorological summer will end tomorrow in a spectacular bang with the arrival of the first “Spanish plume” of the year. Warm air from France and a cold front from the west are forecast to lead to big thunderstorms. The main threat is from hailstones up to 2cm in diameter. There will also be downpours, with up to 25-30mm of rain within an hour, leading to flash floods. Tornados could also appear.